Is there any real-time computer vision system that can learn to detect new objects of new classes?
You are probably looking for incremental learning (sometimes known as lifelong learning) techniques, i.e. machine learning techniques that attempt to address the catastrophic forgetting effect of neural networks when trained incrementally, i.e. as new classes or data are added to the original training data.
There are different techniques and some of them store (or compress) the old data in order to fully or partially re-train the neural network with the new classes or data.  However, note that this is a relatively new area of research and significant progress still needs to be made to produce serious tools. If you are specifically interested in incremental class learning, maybe have a look at this paper Class-incremental Learning via Deep Model Consolidation (2020).